1. Field of the Invention
The present invention relates to a discharge apparatus for a movable hearth type heat treatment furnace and its operation method. The present invention also relates to a method of manufacturing molten iron by reducing raw material formed from at least powdered iron oxide-containing material and powdered carbonaceous reducing agent to manufacture reduced iron using a rotary hearth type reduction furnace and the like as a movable hearth type heat treatment furnace, and then reducing and melting the reduced iron in a molten iron-manufacturing furnace.
2. Description of the Invention
Recently, a movable hearth type heat treatment furnace, for example, a rotary hearth type reduction furnace has been widely used for manufacturing reduced iron or metallic iron by reducing raw material which comprises iron ore or dust of an iron foundry, the other waste, coal and the like as components. The movable hearth type heat treatment furnace for manufacturing reduced iron or metallic iron reduces raw material on the movable hearth or additionally heats raw material after reduced, thereby melting and separating iron and slag. And, although a discharge apparatus is provided for discharging reduced iron that is highly reoxidizable or metallic iron that has no reoxidation problem (to be referred as heat-treated products), carbonaceous powder, and slag mixture, which are discharged from a discharge port out of the furnace, various types of such a discharge apparatus for movable hearth type heat treatment furnace have been known.
For example, a known discharge apparatus consists of a chute located between a discharge port for heat-treated products of movable hearth type heat treatment furnace and a downstream side facility, and high temperature switching valves having two or more stages for preventing outflow of high temperature gas from the movable hearth type heat treatment furnace, the valves having a well-known construction. That is, the discharge apparatus is constructed to feed heat-treated products discharged from the furnace into the downstream side facility simultaneously with discharging heat-treated products out of the furnace, while preventing outflow of high temperature gas from the movable hearth type heat treatment furnace by mutual on-off operations of high temperature switching valves.
In addition, another known discharge apparatus consists of a chute located between the discharge port for discharging heat-treated products of the movable hearth type heat treatment furnace and a detachable sealed container, and high temperature switching valves of well-known construction in the way of chute.
Yet another known discharge apparatus consists of a chute, of which one end is connected to the discharge port for discharging heat-treated products of the movable hearth type heat treatment furnace, and the other end is provided with a quantitative discharge apparatus such as a vibration feeder, a screw conveyor, or a pan conveyor.
Conventionally, molten pig iron was manufactured mainly by a blast furnace method. The blast furnace method is a method in which raw material of massive iron ore and coke are charged from the top portion of furnace and hot reducing gas is produced by blowing hot blast from a tuyere provided in the bottom portion of furnace to burn the coke, thereby reducing and melting the iron oxide. Although the blast furnace method is a process having a very good efficiency, it has a drawback in that it requires massive raw material and reducing agent. That is, because the feeding of massive ore as raw material is tight, it is inevitable to use powdered ore after forming it into sintered ore or pellets and thus a sintering machine or a facility for manufacturing pellets is needed. In addition, because reducing agent is used after carbonized and coked, strongly caking coal that is expensive is needed as coal for manufacturing coke besides a coke furnace. Furthermore, in these facilities, because it is supposed that cost for measuring pollution will be increased suddenly as environmental regulation is strengthened from now on, thereby cost needed for processing raw material and reducing agent in advance will be increased, and as a result, there will be a problem that cost of molten pig iron will be increased.
Recently, methods of manufacturing molten pig iron directly from powdered iron ore and coal material which do not require or simplify a facility for processing such raw material and fuel in advance, have been developed. Among them, it is noted that various methods of manufacturing molten pig iron have been proposed and paid attention, in which a mixture of powdered iron ore and coal material is pre-reduced in the aforementioned movable hearth type heat treatment furnace, for example, a rotary hearth type heat treatment furnace, so that reduced iron is manufactured, and the reduced iron is discharged by the aforementioned discharge apparatus and the like, and then reduced and molten in a smelting furnace.
For example, finely powdered iron ore and finely powdered carbonaceous material are formed into a briquette shape and these formed products are pre-reduced into reduced iron in a rotary hearth furnace as a pre-reduction furnace and are discharged from the furnace at least at a temperature which is not lower than 1000xc2x0 C. Meanwhile, a smelting furnace, within which metallic bath exists and which blows oxygen into the furnace simultaneously introducing finely powdered carbonaceous material onto the surface of bath, is prepared, the aforementioned reduced iron is charged into the smelting furnace, and reducing and melting are performed. In this case, the exhaust gas of smelting furnace is recovered and introduced into a rotary hearth furnace, which is a pre-reduction furnace, as fuel for pre-reducing the formed products.
Also, powdered iron oxide and powdered solid-reducing agent are mixed, the mixture obtained thereby is pre-reduced in the powdered state as it is without being conglomerated thereby producing reduced iron, and then discharged from the furnace at a temperature of at least 500xc2x0 C. Meanwhile, a filled-in layer of coal material exists in the furnace, conglomerated granular coal material is charged from the top portion of the furnace, and the reduced iron is charged into a shaft furnace that generates reducing gas by blowing oxygen-containing gas from a tuyere provided in the bottom portion of the furnace to burn coal material in front of the tuyere, whereby reducing and melting are performed. An this time, some cases recover produced gas of the shaft furnace and charge a part of it into the rotary hearth furnace, which is a pre-reduction furnace, as fuel.
Furthermore, some cases pre-reduce raw pellets consisting of iron ore, carbon-containing reducing agent and slag-forming material to form self-fluxing reduced iron, charge the self-fluxing reduced iron into a submerged arc furnace, and perform reduction and melting while melting and separating slag during a temperature-rising process, thereby manufacturing molten pig iron, of which the concentration of carbon is 1? 5%.
Although the above prior arts are excellent, at first, there are problems in connection with the means for feeding reduced iron discharged from the rotary hearth furnace into the smelting furnace as follows:
Firstly, as to the discharge apparatus of movable hearth type heat treatment furnace, because the heat-treated products discharged from the exhaust port of movable hearth type heat treatment furnace have a high temperature maximum above 1000xc2x0 C. and in addition thereto powder (carbonaceous powder) is also discharged, troubles such as blockage and adherence are liable to be occurred in the high temperature switching valves and it is difficult to continue stable operation. In addition, the discharge of heat-treated products by the high temperature switching valve is intermittent, and in particular there is a problem to be solved in that continuous melting is impossible if a melting furnace is located in the downstream side, whereby improvement in productivity of reduced iron or metallic iron cannot be expected.
In addition, it is difficult to make the movable hearth type heat treatment furnace and the chute located between the movable hearth type heat treatment furnace and the detachable sealed container in a completely sealed construction, and in particular there is a possibility that ambient air may be flown into the movable hearth type heat treatment furnace if the movable hearth type heat treatment furnace is operated under a negative pressure. That is, if ambient air is flown into the movable hearth type heat treatment furnace, there will be such problems that the reduced iron will be reoxidized thereby deteriorating the product value, and simultaneously the reduced iron will be molten and welded or carbonaceous powder will be burnt by heat generated at the oxidation, whereby discharge will be difficult and the product value will be deteriorated.
While there is an advantage in that the heat-treated products can be quantitatively discharged, there is a problem in connection with resistance to high temperature and air tightness in the vibration feeder, screw conveyor, pan conveyor and the like and there is occurred such problems that the reduced iron is reoxidized thereby deteriorating the product value, and simultaneously the reduced iron is molten and welded or carbonaceous powder is burnt by heat generated at the oxidation. Furthermore, although the screw conveyor is most excellent in air tightness among the vibration feeder, screw conveyor, pan conveyor and the like, the screw conveyor has a problem to be solved in that because a screw shaft directly contacts with heat-treated products of high temperature due to its construction, loss caused by abrasion is violent and thus maintenance cost is increased, besides the problem of heat resistance.
Next, although it is rare case, it has been found that foreign substances reached maximum up to tens of centimeters are entrained in the reduced iron. These foreign substances are those dropped from refractory material or accretion, or metallic iron plate produced on the hearth and the like, and it is practically impossible to completely remove these foreign substances.
However, the entrainment of such foreign substances was not considered at all in the prior art and thus it is supposed that there may be problems as follows: as explained in the above, if foreign substances of a large size are entrained in reduced iron, they are entangled in a chute or charging port of shaft furnace, so that blockage is likely to be occurred and the feeding of reduced iron to a smelting furnace will be hindered. In addition, if the internal diameter of chute is enlarged so that foreign substances shall not entangled in the chute, the foreign substances will be charged into the smelting furnace, whereby there will be problems in that if the foreign substances are peeled-off refractory material, they will block a molten pig iron tapping port or a residue discharge port at the time of tapping the molten pig iron or discharging residues, whereby molten pig iron or slag cannot be discharged. And, when melting and smelting are performed using an electrode, it is required to feed reduced iron around the electrode, but if the diameter of chute is too large, the reduced iron is dispersed in the furnace and is not melt so effectively. Also, there may be problems in that the foreign substances contact with and impair the electrode and in that if the foreign substances are nonconductors such as peeled-off refractory material, they hinder the flow of electricity, thereby causing deterioration of productivity.
Furthermore, in connection with dealing with the influences to be happened to the operation of rotary hearth furnace, when the amount of gas produced in a smelting furnace is varied either due to variations in the amount of reduced iron fed to the smelting furnace and metallization rate, or due to an abnormal operation when tapping molten pig iron, discharging residues from the smelting furnace and the like, no measure was taken into consideration at all.
It is an object of the present invention to provide a discharge apparatus for movable hearth type heat treatment furnace, which can quantitatively and continuously discharge reduced iron, without hindering the operation of movable hearth type heat treatment furnace and a downstream side facility, and without reoxidizing the reduced iron even when discharging reduced iron which is highly reoxidizable, and furthermore which can reduce the wearing-out of constituent components, and to provide a method of operating the movable hearth type heat treatment furnace.
And, it is another object of the present invention to provide a method and apparatus for manufacturing molten pig iron using a combination of a rotary hearth furnace and a smelting furnace, wherein reduced iron manufactured in the rotary hearth furnace can be continuously fed into the smelting furnace in a state of high temperature while preventing foreign substances from being charged into the smelting furnace and produced gas generated in the smelting furnace may be efficiently used as reducing fuel for the rotary hearth furnace without influencing the operation of the rotary hearth furnace even if the amount of the produced gas is varied.
The present invention is a discharge apparatus for a movable hearth type heat treatment furnace which discharges heat-treated products from the movable hearth type heat treatment furnace to a downstream side facility, characterized in that the discharge apparatus comprises, in a casing, a recessed retaining member provided with a receiving recess for receiving and temporarily retaining the heat-treated products discharged from said movable hearth type heat treatment furnace, and a scraper that reciprocates along a surface of said receiving recess and discharges said heat-treated products retained in the receiving recess into said casing.
Said discharge apparatus is the discharge apparatus for a movable hearth type heat treatment furnace characterized in that a seal leg is provided between said movable hearth type heat treatment furnace and said recessed retaining member, for introducing the heat-treated products discharged from said movable hearth type heat treatment furnace into the receiving recess of said recessed retaining member.
Said discharge apparatus is the discharge apparatus for a movable hearth type heat treatment furnace characterized in that a gas blowing nozzle for blowing anti-reoxidation gas into said casing is communicated with said seal leg.
Said discharge apparatus is the discharge apparatus for a movable hearth type heat treatment furnace characterized in that a screen sizer is provided between said movable hearth type heat treatment furnace and said seal leg, for sorting foreign substances in the heat-treated products and discharging them out of the system
The present invention is an apparatus for manufacturing molten iron characterized in that it comprises a movable hearth type heat treatment furnace for obtaining reduced iron by reducing raw material formed by mixing at least powdered iron oxide-containing material and powdered carbonaceous reducing agent, a sorting means for removing foreign substances entrained in said reduced iron discharged from said movable hearth type heat treatment furnace, and a molten iron-manufacturing furnace for obtaining molten iron by melting said reduced iron in which said foreign substances have been removed by the sorting means.
Said apparatus for manufacturing molten iron is characterized in that it comprises a feeding means for feeding said reduced iron to said molten iron-manufacturing furnace while maintaining the seal portion with said reduced iron in which said foreign substances have been removed by said sorting means.
Said apparatus for manufacturing molten iron is characterized in that said feeding means feeds said reduced iron to said molten iron-manufacturing furnace by said discharge apparatus.
Said apparatus for manufacturing molten iron is characterized in that it comprises a gas recovery means for introducing at least a part of produced gas generated in said molten iron-manufacturing furnace into said movable hearth type heat treatment furnace as fuel for reduction.
Said apparatus for manufacturing molten iron is characterized in that said gas recovery means introduces said produced gas into the first half of reduction of said movable hearth type heat treatment furnace.
Said apparatus for manufacturing molten iron is characterized in that said gas recovery means introduces said produced gas into the second half of reduction of said movable hearth type heat treatment furnace.
Said apparatus for manufacturing molten iron is characterized in that said gas recovery means comprises a means for removing dust from the produced gas.
Said apparatus for manufacturing molten iron is characterized in that said gas recovery means comprises a means for cooling the produced gas.
Said apparatus for manufacturing molten iron is characterized in that said gas recovery means comprises a means for regulating the amount of produced gas.
Said apparatus for manufacturing molten iron is characterized in that said movable hearth type heat treatment furnace is a rotary hearth type reduction furnace.
The present invention is a method of operating a movable hearth type heat treatment furnace which discharges heat-treated products from the movable hearth type heat treatment furnace to a downstream side facility, characterized in that the method comprises steps of: receiving and temporarily retaining the heat-treated products discharged from said movable hearth type heat treatment furnace in a receiving recess of a recessed retaining member provided in a casing; and reciprocating a scraper along a surface of said receiving recess, so that said heat-treated products retained in said receiving recess are discharged into said casing.
Said method of operating a movable hearth type heat treatment furnace is characterized in that anti-reoxidation gas which at least prevents reoxidation of heat-treated products is blown into said casing.
Said method of operating a movable hearth type heat treatment furnace is characterized in that the heat-treated products discharged from said movable hearth type heat treatment furnace are received in the receiving recess of said recessed retaining member through the internal of said seal leg.
Said method of operating a movable hearth type heat treatment furnace is characterized in that a blowing amount of anti-reoxidation gas blown into said casing is controlled according to a surface temperature of said heat-treated products.
Said method of operating a movable hearth type heat treatment furnace is characterized in that discharge amount of the heat-treated products is controlled by regulating the reciprocation number per hour of said scraper.
The present invention is a method of manufacturing molten iron characterized in that it comprises a reduction step of reducing raw material formed by mixing at least powdered iron oxide-containing material and powdered carbonaceous reducing agent to obtain reduced iron, a sorting step of removing foreign substances entrained in the reduced iron discharged from the reduction step, and a melting step of melting said reduced iron in which said foreign substances have been removed in the sorting step, thereby obtaining molten iron.
Said method of manufacturing molten iron is characterized in that it comprises a feeding step of feeding said reduced iron to said melting step while forming and maintaining the seal portion with said reduced iron in which said foreign substances have been removed in said sorting step.
Said method of manufacturing molten iron is characterized in that said feeding step feeds said reduced iron to said molten iron-manufacturing furnace using said discharge apparatus.
Said method of manufacturing molten iron is characterized in that it comprises a gas recovery step of introducing at least a part of produced gas generated in said reduction step to said reduction step as fuel for reduction.
Said method of manufacturing molten iron is characterized in that said gas recovery step introduces said produced gas at the first half of said reduction step.
Said method of manufacturing molten iron is characterized in that said gas recovery step introduces said produced gas at the second half of said reduction step.
Said method of manufacturing molten iron is characterized in that said gas recovery step comprises a step of removing dust from the produced gas.
Said method of manufacturing molten iron is characterized in that said gas recovery step comprises a step of cooling the produced gas.
Said method of manufacturing molten iron is characterized in that said gas recovery step comprises a step of regulating the amount of produced gas.
Said method of manufacturing molten iron is characterized in that in said reduction step, reduction is performed by a movable hearth type heat treatment furnace.
Said method of manufacturing molten iron is characterized in that said reduction step, reduction is performed by a rotary hearth type heat treatment furnace.
According to the present invention, it is possible to continuously perform a stable operation. Furthermore, because the discharge of heat-treated products is performed by reciprocating the scraper, an intermittent interval is short as compared to a high temperature switching valve and because the heat-treated products can be fed into the melting furnace of downstream side in a condition more close to continuation, continuation of stable operation is possible, whereby the productivity of reduced iron or metallic iron is excellent.
Furthermore, because the possibility that oxidative gas such as the ambient air leaks into the movable hearth type heat treatment furnace is reduced even if the movable hearth type heat treatment furnace is operated under a negative pressure due to the construction that blocks the inflow of air into the movable hearth type heat treatment furnace by the material seal function of the seal leg and the blowing of anti-reoxidation gas in the discharge apparatus, there will be no such problem that reduced iron will be molten and welded or carbonaceous powder will be burnt by heat generated at the oxidation, without reoxidation of reduced iron, whereby it is possible to manufacture products excellent in quality.
And, because the scraper in the form of plate is simple in construction, its contact pressure is low, and its wearing amount is small, an excellent economic effect can be obtained in that maintenance cost can be considerably lowered.
According to the present invention, it is possible to continuously feed reduced iron in the state of high temperature to the melting step (molten iron-manufacturing furnace) while preventing the charge of foreign substances from the reduction step (rotary hearth type reduction furnace) into the molting step (molten iron-manufacturing furnace). By this, it is possible to continuously manufacture molten iron of stable quality in low cost without stopping the operation.
And, in addition to the above effects, it is possible to continuously feed reduced iron to the melting step (molten iron-manufacturing furnace) while preventing reoxidation of reduced iron without causing inflow of the ambient air into the reduction step (rotary hearth type reduction furnace) even if the ambient air leaks into the melting step (molten iron-manufacturing furnace).
Moreover, produced gas generated in the melting step (molten iron-manufacturing furnace) can be efficiently used as reducing fuel of the reduction step (rotary hearth type reduction furnace).
According to the present invention, the problem of reoxidation of reduced iron is not caused even if a little ambient air is entrained in the produced gas generated in the melting step (molten iron-manufacturing furnace).
Also, it is possible to use the produced gas generated in the melting step (molten iron-manufacturing furnace) and containing dust, as fuel gas, after purifying it.
Furthermore, it is not required to make a facility following the produced gas-cooling step (produced gas-cooling means) to a specification of high temperature and is possible to make it compact.
According to the present invention, it is possible to use the produced gas generated in the melting step (molten iron-manufacturing furnace) as reducing fuel for the reduction step (rotary hearth type reduction furnace) without influencing the operation of reduction step (rotary hearth type reduction furnace) even if its amount is fluctuated.